Genotype by environment interaction for milk yield in Sarda dairy sheep

Abstract

Genotype by environment interaction (GEI) for milk yield (ME) was investigated by analyzing 40 140 first lactation records performed in 538 flocks. Flock-year effects from national genetic evaluation were used to define low (L), medium (M) and high (H) yielding environments. Differences observed between adjacent subsets were approximately 20% of the trait overall mean. Sire variance components estimated using multitrait analysis were 58, 82 and 149% of the estimate from the complete dataset (L, M and H, respectively) and genetic correlation coefficient between extreme subsets was 0.66, lower than genetic correlations obtained from randomly sampled subsets. Rank correlation coefficients between estimated transmitting abilities (ETA), obtained independently within L, M and H subsets for 71 AI rams having at least 10 daughters per subset, were lower than one (ranging from 0.42 to 0.56). These results strongly supported the existence of GEI for milk yield in Sarda sheep flocks. The influence of GEI on phenotypic responses in flocks differing in yield level could be due to a reduced expression of genes under conditions of restricted environmental opportunity. Splitting the selection scheme according to farming conditions does not seem a suitable solution for the Sarda breeding program. Thus, to provide farmers with genotypes suitable to exhibit a good phenotypic expression in different conditions, the selection across all environments, in which the descendants are expected to perform, still seems the best option. ZusammenfassungGenotyp-Umwelt-Interaktion für Milchleistung bei Sarda Milchschafen Die Genotyp-Umwelt-Interaktion (GEI) fü r Milchleistung (ME) wurde anhand von 40.140 Aufzeichnungen der Erstlaktation in 538 Herden untersucht. Offiziell erfasste Daten zu Herdenund Jahreseffekten wurden verwendet, um niedrige (L), mittlere (M) und hohe (H) Leistungen in Abhängigkeit von der Umwelt zu definieren. Zwischen benachbarten Teilgruppen beobachtete Unterschiede betrugen etwa 20% vom Gesamtdurchschnitt. Erwartete Vater-Varianz-Komponenten, berechnet mithilfe multivariabler Analyse, lagen bei 58, 82 und 149% des Gesamtdatensatzes fü r die Leistungen von L, M und H in Abhängigkeit von der Umwelt. Der genetische Korrelationskoeffizient zwischen extremen Teilgruppen betrug 0,66 und war damit niedriger als die genetischen Korrelationen von zufällig gesammelten Teilgruppen. Rangkorrelationskoeffizienten zwischen Ü bertragungswahrscheinlichkeiten (ETA), die fü r 71 AI Bö cke innerhalb L, M und H beobachtet wurden und die mindestens 10 Tö chter pro Teilgruppe hatten, waren kleiner als eins (0,42 bis 0,56). Diese Ergebnisse bestärkten die Existenz einer Genotyp-Umwelt-Interaktion (GEI) fü r Milchleistung bei Schafherden der Rasse Sarda. Der Einfluss der Genotyp-Umwelt-Interaktion auf die Ausprägung des Phänotypes in Herden, die sich in der Milchleistung unterschieden, kö nnten auf einer reduzierten Expression von Genen durch eine ungü nstigere Umwelt beruhen. Das Teilen des Selektionsschema aufgrund von unterschiedlichen Haltun...

Factors affecting milk yield and ewe's lactation curves estimated with test-day models

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Genotype by environment interaction and model comparison for growth traits of Santa Ines sheep

“…In general, the model choice had implications in the selection of the best animals, particularly when considering different environments. Sanna et al (2002), in a study with Sarda dairy sheep, pointed out changes in genotype ranking, as well as changes in the absolute and relative magnitude of variance between environments, suggesting the existence of G9E for milk yield in rearing conditions.…”

Maternal Inheritance and Rapid Evolution of Sexual Size Dimorphism: Passive Effects or Active Strategies?

“…When such strong maternal effects differ between the sexes, they can bias evolution of sexual size dimorphism in several ways (Rutledge et al 1972;Lande and Kirkpatrick 1990;Meyer 1992;Quintanilla et al 1999;Sanna et al 2002). First, the interaction (negative or positive) between maternal effects and additive genetic variance in either sex can bias a trait response to selection.…”